A baghouse (“BH”) unit, also called a fabric filter unit, is used as an air pollution control device and functions to capture particulate matter from flue gas streams of coal-fired electricity generating plants or waste-burning industrial boilers. Particulate matter in flue gas streams may include fly ash from the boiler, sorbents and other conditioning agents added to capture contaminants in the stream such as mercury, hydrochloric acid (HCl), bromine, and others. BH units are highly efficient particulate collection devices, operating effectively in a broad range of incoming loading or particle size. Further, BH units may serve as dry collection devices for removing contaminant gases and heavy metals via increased exposure to adsorbents. Recently many sites have begun to use the TOXECON™ system that utilizes both an electrostatic precipitator (“ESP”) and BH unit. In this system, a sorbent, used to capture especially mercury, is injected downstream from the ESP unit such that fly ash can be collected in the ESP and sold to concrete producers. BH units in these systems serve to capture remaining particulate matter, sorbent, and contaminants from the flue gas stream prior to emission from the stack serving as the last emission control device. The TOXECON™ system is described in U.S. Pat. No. 5,505,766 by Chang, which is incorporated herein by reference in its entirety.
In the United States and Canada, federal and state/provincial regulations have been implemented or are being considered to reduce mercury emissions, particularly from coal-fired power plants, steel mills, cement kilns, waste incinerators and boilers, industrial coal-fired boilers, and other coal-combusting facilities. For example, the United States Environmental Protection Agency (U.S. EPA) has promulgated Mercury Air Toxics Standards (MATS), which would among other things require coal-fired power plants to capture at least approximately 80% to 90% of their mercury emissions. The rule applies to four pollutant classes: mercury (Hg), acid gasses such as sulfur dioxide (SO2) and hydrochloric acid (HCl), filterable particulate matter (fPM), and non-mercury metals.
The leading sorbent for mercury control from coal-fired power plants is activated carbon. Activated carbon, particularly powder activated carbon (“PAC”), can be injected into the flue gas emitted by the boiler of a power plant. PAC is a porous carbonaceous material having a high surface area, which exposes significant amounts of beneficial chemically functional and reaction sites and which creates high adsorptive potential for many compounds, including capturing mercury from the flue gas.